1. Field of Invention
This invention relates to an apparatus for molding plastic objects which utilizes a needle in a valve of a liquid plastic injection unit as an ejector pin for ejecting the plastic object from the mold. More specifically, this invention relates to an apparatus in which the valve is modified such that additional ejector pins may be positioned in close proximity to the needle.
2. Description of the Prior Art
It is common to mold plastic objects (e.g. plastic containers and mini-disk cartridge shells) using an apparatus incorporating a number of metal plates. As shown in FIGS. 14-19, such an apparatus may include a core plate 30', a cavity plate 40' and an ejector plate 20'. Carved out areas in the interiors of the core plate and the cavity plate form the cavity of the mold when these are mated. Referring to FIGS. 14-16, the conventional molding devices position the ejector plate behind the cavity plate. A plurality of ejector pins 22' extend outwardly from the ejector plate and pass through holes in the cavity plate. Thus, when the ejector plate is moved forward the ejection pins are urged against any newly molded part in the cavity plate, thereby forcing the part out of the cavity plate. Therefore, when the ejector plate is moved forward, the ejector pins are urged against any newly molded part in the cavity plate, thereby forcing the part out of the cavity plate.
Typically, liquid plastic is injected from a supply line 70' coming from an injection unit into the mold through one or more openings in the core plate. The flow of liquid plastic material may be controlled by a valve 60' having a nozzle 62' and a needle 64' within the nozzle. The movement of the needle in to and out of the valve opening controls the flow of liquid plastic into the mold's cavity 52'. Movement of the needle may be controlled, for example, by a small hydraulic or air valve cylinder 66'. When the tip 65' of the needle is flush with the end 67' of the nozzle, the valve is closed (See FIG. 11). When the small cylinder retracts the needle, the valve is opened (See FIG. 12) and liquid plastic material is allowed to enter the cavity of the mold. After the cavity of the mold has been filled, the valve cylinder pushes the needle forward to the closed position (See FIG. 11), such that the tip of the needle is again flush with the end of the nozzle.
As shown in FIG. 14, the cavity plate 40' and core plate 30' form the cavity of the mold, as the liquid plastic is dispersed into it through the valve 60'. Referring to FIG. 15 after the plastic material has partially cooled, the cavity plate and the ejector plate both move in tandem away from the core plate, which remains stationary. This causes the molded plastic object 50' to be removed from the core plate. Finally, as shown in FIG. 16, a large hydraulic or air cylinder 24' pushes the ejector plate forward such that all of the ejector pins 22' simultaneously dislodge the molded plastic object from the cavity plate. This sequence of events may be repeated for the next plastic object. Unfortunately, the movement of the ejector pins against the partially cooled plastic part usually results in a blemish being produced at the point of contact. This blemish is on the opposite side of the object, which has received a blemish produced by the injector nozzle.
Most plastic parts have an appearance side, usually the front side, in which a label or some other form of identification is placed. In most present molding processes, as described above, blemishes are left on this appearance side by either the valve or the ejector pins. Manufacturers of these parts have, therefore, typically placed paper labels over the appearance side surface as a means of identifying the object and as a means of covering the blemishes. Due to the increased use of silk screening on plastic objects, a method of molding has recently been developed that allows a plastic object to have an appearance side surface which remains unblemished during the molding process such that, for example, a substantial portion of the appearance side surface may be silk screened.
As is shown in FIGS. 17-19, this innovative molding method positions the injection valve 60' and the ejector pins 22' on the same side of the plastic object 50' to be molded such that only the non-appearance side of the object has blemishes caused by the operation of the injector valve and ejector pins. This is made feasible by utilizing the needle 64' within the valve as an additional ejector pin. By using the needle as an ejector pin, proper positioning of the pins may be maintained to assure that the plastic object does not become warped as it is pushed out of the mold.
Though many configurations are possible, the molding device may include a core plate 30', a cavity plate 40', and an ejector plate 20'. Like the conventional plastic molding devices, the core plate and the cavity plate are mated together to form the mold's cavity. However, unlike conventional devices, the ejector plate is positioned on the side of the core plate opposite the cavity plate. In this embodiment, the core plate, not the cavity plate, has holes or apertures in its side wall which are evenly distributed and the carved out area side wall of the cavity plate should be smooth and/or have a clean finish. The ejector pins extending perpendicularly from the ejector plate's surface are positioned such that each is aligned with a corresponding hole in the core plate. The ends of the injector pins remain flush with the surface of the core plate until the ejector pins are activated to eject the plastic part.
As shown in FIGS. 11-13, an injection unit (not shown) which injects the mold material into the cavity of the mold is connected to the core plate with a flange 75'. The liquid plastic is dispersed through the injection unit via a valve 60', which is encompassed within the flange, having a nozzle 62' on its end. A needle 64' extends through the valve and into the nozzle such that it may serve two purposes. First, referring to FIGS. 11 and 12, the needle performs its conventional function by being utilized to control the flow of liquid plastic material into the cavity of the mold. Second, as shown in FIG. 13, the needle is also employed as an ejector pin by being coupled to the ejection plate so that it may be pushed past the flush point of the end 67' of the nozzle during the process of ejecting the finished plastic part.
As shown in FIG. 18, when the plastic material has partially cooled, the cavity plate moves away from the stationary core plate to remove the finished plastic part from the cavity plate. Next, referring to FIG. 19, the ejector plate is pushed forward so that both the needle and the ejector pins move into the holes in the core plate's side walls simultaneously, thereby dislodging the plastic part from the core plate.
Since the valve nozzle and ejector pins are positioned on the core plate side of the plastic part, which may be referred to as the "non-appearance side" or "back side," the other side of the plastic part, the "appearance side" or "front side", is molded without any marks. Therefore, the entire surface of the appearance side may be silk screened or used for other purposes requiring a smooth surface.
Though this innovative molding method has been found to perform considerably well as providing a means of molding a plastic object with one side remaining; unblemished, a problem sometimes exists. As shown in FIGS. 20 and 21, the ejector pins are positioned around the valve which includes the valve body and the flange. Due to the valve body and flange often occupying a substantial amount of space parallel to the object's surface, the positioning of the ejector pins and the number of pins which may be utilized is limited. Since the number of ejector pins used and their proper spacing relative to the plastic object's surface is imperative to ensure the prevention of warpage to the object, these limitations may result in a corrupted finished product.